In a producing apparatus of a semiconductor, for example, a chemical treatment such as etching is carried out in a vacuum chamber. At this time, a vacuum pump is used for reducing pressure in the vacuum chamber and a pressure regulating valve is used for controlling the vacuum pump. FIG. 17 shows a known vacuum pressure regulating valve. This valve includes a first main port 1 and a second main port 2 connected to a vacuum pump and a vacuum chamber, a valve seat 4 formed around a port hole 3 of the first main port 1, a disc-shaped valve member 5 having an annular sealing member 6 for opening and closing the valve seat 4 on a front face of the member 5, and an air cylinder mechanism 7 for causing the valve member 5 to carry out opening and closing operations.
A regulating shaft portion 5a in the shape of a cylindrical column is formed inside the annular sealing member 6 on the front face of the valve member 5 and a regulating hole portion 3a of such a size that the regulating shaft portion 5a can be fitted in the portion 3a with a clearance between them is formed at an end portion of the port hole 3. A throttle-like member is formed by fitting of the regulating shaft portion 5a in the regulating hole portion 3a when the valve member 5 opens and closes the valve seat 4 and the valve seat 4 is gradually opened and closed by the action of the throttle to thereby enhance controllability of a flow rate at a stage of a small opening degree of the valve member 5.
However, the structure in which the regulating shaft portion 5a in the shape of the cylindrical column is formed on the front face of the valve member 5 and is fitted in the regulating hole portion 3a formed at the end portion of the port hole 3 complicates the shape of the valve member 5, increases the weight of the valve member 5, and impairs workability and operability. Moreover, such also affects the flow rate characteristic when the valve member 5 fully opens the valve seat 4. In other words, the shape of the opening when the valve member 5 is fully open approximates a cylinder formed with an outside diameter D4 of the regulating shaft portion 5a, an inside diameter D5 of the regulating hole portion 3a, and a distance X from an end of the valve seat 4 or the regulating hole portion 3a to the regulating shaft portion 5a. Because both the regulating shaft portion 5a and the regulating hole portion 3a have smaller diameters than a seat diameter D6, the opening area of a flow path is subject to constraints by the regulating shaft portion 5a and the regulating hole portion 3a. 